Society for Conservation Biology Managing the Abundance and Diversity of Breeding Bird Populations through Manipulation of Deer Populations Author(s): William J. McShea and John H. Rappole Source: Conservation Biology, Vol. 14, No. 4 (Aug., 2000), pp. 1161-1170 Published by: Wiley for Society for Conservation Biology Stable URL: http://www.jstor.org/stable/2642012 . Accessed: 12/10/2014 07:34 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Wiley and Society for Conservation Biology are collaborating with JSTOR to digitize, preserve and extend access to Conservation Biology. http://www.jstor.org This content downloaded from 98.233.92.162 on Sun, 12 Oct 2014 07:34:15 AM All use subject to JSTOR Terms and Conditions Managing the Abundance and Diversity of Breeding Bird Populations through Manipulation of Deer Populations WILLIAMJ. McSHEA*AND JOHN H. RAPPOLE National Zoological Park, Conservation and Research Center, Front Royal, VA 22630, U.S.A. Abstract: Deer densities in forests of eastern North America are thought to have significant effects on the abundance and diversity of forest birds through the role deer play in structuring forest understories. We tested the ability of deer to affect forest bird populations by monitoring the density and diversity of vegeta- tion and birds for 9 years at eight 4-ha sites in northern Virginia, four of which were fenced to exclude deer. Both the density and diversity of understory woody plants increasedfollowing deer exclosure. The numerical response of the shrubs to deer exclosure was significantly predicted by the soil quality (ratio of organic car- bon to nitrogen) at the sites. Bird popuilations as a whole increased following exclosure of deer, particularly for ground and intermediate canopy species. The diversity of birds did not increase significantly following ex- closure of deer, however, primarily because of replacement of species as understory vegetation proceeded through successional processes. Changes in understory vegetation accountedfor most of the variability seen in the abundance and diversity of bird populations. Populations of deer in protected areas are capable of causing significant shifts in the composition and abundance of bird communities. These shifts can be re- versed by increasing the density and diversity of understory vegetation, which can be brought about by re- ducing deer density. Manejo de la Abundanciay Diversidadde Aves ReproductorasMediante la Manipulaci6nde Poblaciones de Venados Resumen: Se considera que las densidades de venados en los bosques del Este de Norte Ame'rica tienen efec- tos sign ificativos en la abundancia y diversidad de aves debido al papel que el venado juega en la estructur- aci6n del sotobosque. Evaluamos la habilidad del venado para afectar las poblaciones de aves mediante el monitoreo de la densidad y diversidad de la vegetaci6n y las aves por niueve anos en ocho sitios de 4 ha de extensi6n en el norte de Virginia, cuatro de los cuales fueron cercados para excluir a los venados. Tanto la densidad como la diversidad de lasplantas leniosas del sotobosque incrementaron despues de la exclusi6n de los venados. La respuesta numerica de los arbustos a la exclusi6n de venadosfue pronosticada significativa- mente por la calidad del suelo (proporci6n de carbono orgdnico/nitr6geno) en los sitios. Las poblaciones de aves en su conjunto incrementaron despues de la exclusi6n de venados, particularmente las especies del suelo y de dosel intermedio. Sin embargo, la diversidad de aves no increment6 sign ificativamente despues de la exclusi6n de venados, primariamnente debido al remplazo de especies alpasar la vegetaci6n del sotobosque por los procesos sucesionales. Los cambios en la vegetaci6n del sotobosquefueron responsables de la mayoria de la variabilidad observada en la abundancia y diversidad de poblaciones de aves. Las poblaciones de ve- nados en dreas protegidas son capaces de causar cambios significativos en la composici6n y la abundancia de comunidades de aves. Estos cambios pueden ser revertidos al incrementar la densidad y diversidad de la vegetaci6n del sotobosque, lo cualpuede llevarse a cabo mediante una reducci6n en la densidad de venados. *email [email protected] Paper submitted April 22, 1999; revised manuiscript accepted October 13, 1999. 1161 Coniservation Biology, Pages 1161-1170 Voluime 14, No. 4, August 2000 This content downloaded from 98.233.92.162 on Sun, 12 Oct 2014 07:34:15 AM All use subject to JSTOR Terms and Conditions 1162 Effectsof Deeron Fo1estBirds McShea& Rappole Introduction (McShea & Rappole 1992, 1997; deCalesta 1994; McShea et al. 1995). This hypothesis is based on the facts that Ungulate populations have strong direct and indirect im- deer are often the principal agent of structural change pacts on forest plant communities (Augustine & Mc- within forests and that many species of birds are sensi- Naughton 1998). These changes are brought about both tive to such changes. Deer are not the only cause of for- by browsing (Alverson et al. 1988; Tilghman 1989; Au- est alteration, but within protected forests most other gustine & Frelich 1998) and by the indirect cycling of factors (e.g., timber harvest and wildfires) have been nutrients and energy flow (Pastor & Naiman 1992; Hobbs eliminated. 1996). The result of these activities is to change the spe- Earlierstudies have found circumstantial evidence that cies composition and relative abundance of both herba- bird populations are sensitive to deer densities. Declines ceous and woody plants within forest ecosystems. In the in Ovenbirds in a western Marylandpreserve (Boone & United States, most states report deer densities that ex- Dowell 1986) and declines in understory birds in New ceed all previous estimates for the century (McCabe & York (Baird 1990) were attributed to high deer densi- McCabe 1997). This increase is the direct result of con- ties, and lower numbers of individuals in all bird guilds servation efforts to increase the number of these and in a Pennsylvania preserve were attributed to large her- other game species. How planned increases in large her- bivores (Casey & Hein 1983). These studies, however, bivores affect other forest animal species is unknown. noted only that declines in bird species and numbers of White-tailed deer (Odocoileus virginianus), however, individuals coincided with more deer. Kentucky War- may play an increasing role in the structuring of forest bler (Oporornisformosus) densities were tracked for 10 ecosystems and should be considered a significant factor years at the National Zoo's Conservation and Research in plans for protected forest management plans (Porter Center in Virginia, and over that period the distribution & Underwood 1999). of territories shifted to areas that maintained low deer Food webs are complex interactions between species densities (McShea et al. 1995). The most complete study that regulate the transfer of nutrients and energy across was deCalesta's (1994) bird survey of several deer enclo- trophic levels (Polis & Strong 1996). Dominant or key- sures in Pennsylvania. After 10 years at predetermined stone organisms not only influence adjacent trophic lev- deer densities, point-count surveys revealed higher en- els but have effects that are measurable throughout an counter rates for intermediate canopy birds within areas ecosystem (Power 1992; Power et al. 1996). If habitat with the lowest deer densities. The experiment, how- characteristics influence the distribution of most animal ever, was designed primarily to examine the effects of species, and if ungulates shape habitat characteristics, deer on forestry practices, so bird densities were not then ungulates may have an important role in complex monitored during the first 10 years of the study, and the food webs throughout multiple trophic levels. Food enclosures contained a mixture of managed and unman- web links have been demonstrated between white-tailed aged forest. DeGraaf et al. (1991) examined the interac- deer and small mammals (Ostfeld 1997; McShea 2000) tion between high deer density and forest management and among white-tailed deer, white-footed mice (Per- on forest bird communities. They found that the effects omyscus leucopus), and ticks (Ixodes scapularis) (Jones of thinning were more obvious than those of deer densi- et al. 1998). These linkages suggest that the foraging be- ties, but Hermit Thrushes (Catharus guttatus) were havior of deer may structure forest populations of other more abundant and Eastern Towhees were less abun- animal species. dant at low deer densities. These studies point to the Bird species are particularly sensitive to changes in need to quantify how forest birds respond to changes in vegetation volume and composition (Mills et al. 1991). deer density in order to manage effectively a group of Direct positive correlations have been found between species that has been declining over the same period bird diversity and vegetation volume in tropical forest that deer densities have been increasing. Efforts by gov- systems (Bell 1982) and spatial heterogeneity in temper-